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We’ve entered the fall campaign season, and we’re starting to get a clearer sense of the lay of the political land for 2020: There are just three or four Democrats who’ll have the chance to take on Donald Trump, where the battle will be over just three or four states.

First, it is true that the Democratic field has winnowed, and not just because a few of the stragglers have (mercifully) dropped out. Historical data bear this out.

According to Washington Post columnist and data analyst David Byler, “Candidates who led a simple average of the last five polls about six months before Iowa won the nomination a little over half of the time.” That’s good news for Biden. But Byler also goes on to note that “in recent primaries where an early poll leader failed to secure the nomination, the eventual winner tended to still come from the top tier.”

Along those lines, analysts are now suggesting it’s a three-way race between Biden, Elizabeth Warren, and Bernie Sanders, but I’m not ready to write off Kamala Harris as the younger, more charismatic, albeit long-shot alternative. Despite her failure to keep pace in the polls with the other three so far, Harris retains a plausible path to the nomination.

The next question to interrogate is whether “almost anybody” can beat Donald Trump in 2020. Right now, polls suggest that each of the top four Democrats will thump Trump by double digits.

To put it bluntly, I’m not buying it. An election is a choice between two people, and—these days—we’re just way too polarized a country for one candidate to beat the other by five points, let alone 15.

The mistake is to assume the current “snapshot” is predictive of what the world will look like in November of 2020. The problem is that the world is dynamic, not static. Now, it’s entirely possible that environmental factors (such as a recession) could benefit Democrats. But it’s true that while Democrats want 2020 to be a referendum, Donald Trump will work overtime to make it a binary choice.

Consider this: What might a Democratic nominee look like after Trump and his supporters have been attacking him or her for seven or eight months, assuming a nominee is more-or-less known by March or April?

If Biden is the nominee, you can expect a lot of focus on his gaffes and fabrications—which is one reason Biden really needs to tone that down. If it’s Bernie Sanders, this election will be about the rise of socialism. If it’s Elizabeth Warren, “Pocahontas” will be invoked as mockery—and as a substantive critique on Warren’s honesty and authenticity. Make no mistake, this will move the numbers. Remember, Michael Dukakis was polling at 55 percent of the vote as late as July of 1988. That was before George H.W. Bush’s team went to work on him. Dukakis dropped 10 points by election time.

The question is, who can endure these predictable attacks. The answer is Biden. By virtue of being a universally known commodity, he is the least susceptible to attrition. It’s also true that he plays best in the states that will likely matter most in 2020—which is my next point.

Trump can win the election without winning the popular vote. As such, polls showing Democrats consistently ahead, even if they are accurate (and durable), are still somewhat misleading.

So how can a Democrat win the Electoral College? Two data points seem relevant.

First, according to the Washington Post’s Dan Balz, “Just four states are likely to determine the outcome in 2020. Each flipped to the Republicans in 2016, but President Trump won each by only a percentage point or less. The four are Pennsylvania, Michigan, Wisconsin, and Florida. Many analysts point to Wisconsin as the single state upon which the election could turn.”

Second, the Philadelphia Inquirer’s look at Obama-Trump voters suggests that at least as many as one-third of the working-class white voters in places like Pennsylvania might be willing to vote Democratic again in 2020—if the party nominates a moderate. The most obvious path to the White House, it seems to me, involves flipping these voters.

“If Democrats are smart, they will bet big on the best horse they’ve got.”

Based on this premise, Biden is the clearly the best positioned to win the presidency, because he hails from Pennsylvania, because of his unmatched experience, and because of the folksy image as a moderate. But even if you disagree with these educated assumptions—even if you think the key isn’t working-class whites in the Rust Belt, but rather, increasing African-American turnout—does anyone believe that Sanders or Warren would have a better shot at doing that than Barack Obama’s vice president—especially if he were to pick an exciting running mate?

There are plenty of reasons to think the smart money is still on Trump to be re-elected—especially if he can stave off a recession. Democrats do have a shot at defeating him, but the danger for Democrats is overconfidence. If they think any candidate would easily destroy Trump, they might make the mistake of nominating… any candidate.

So far, this quixotic notion hasn’t taken root, as Biden is so far doing well with it, even after some embarrassing stumbles. But narratives have a way of taking off, and we are entering into the heart of the primary campaign.

The good thing about primary campaigns is that there’s always the chance that a frontrunner will be revealed to have a glass jaw, or that some dark horse will emerge as the obvious choice. That hasn’t happened. Labor Day is over, and we are entering into a more serious phase of the campaign.

Joe Biden is far from perfect. But in 2020, it is very clear that no Democrat has a better chance of winning the presidency than him. If Democrats are smart, they will bet big on the best horse they’ve got. Biden is—by far—the best Democrat for this job.